I carry one of these most days - a Lowepro Topload Zoom Mini -- fits my Nikon with a 18-70mm lens or a 50mm prime. I basically use it as is or put it in my bag. I wanted something minimal, light and yet worked if I wanted to use a bag off the bike as well. It'll only fit your camera with a lense on and you'd have to carry spare lenses separately but when I'm riding, I only bring one lense with me anyway.